Compositions and methods for chemical-mechanical polishing (CMP) of the surface of a substrate are well known in the art. Polishing compositions (also known as polishing slurries, CMP slurries, and CMP compositions) for CMP of surfaces of semiconductor substrates (e.g., integrated circuits) typically contain an abrasive, various additive compounds, and the like.
In general, CMP involves the concurrent chemical and mechanical abrasion of surface, e.g., abrasion of an overlying first layer to expose the surface of a non-planar second layer on which the first layer is formed. One such process is described in U.S. Pat. No. 4,789,648 to Beyer et al. Briefly, Beyer et al., discloses a CMP process using a polishing pad and a slurry to remove a first layer at a faster rate than a second layer until the surface of the overlying first layer of material becomes coplanar with the upper surface of the covered second layer. More detailed explanations of chemical mechanical polishing are found in U.S. Pat. Nos. 4,671,851, 4,910,155 and 4,944,836.
In conventional CMP techniques, a substrate carrier or polishing head is mounted on a carrier assembly and positioned in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate, urging the substrate against the polishing pad. The pad and carrier, with its attached substrate, are moved relative to one another. The relative movement of the pad and substrate serves to abrade the surface of the substrate to remove a portion of the material from the substrate surface, thereby polishing the substrate. The polishing of the substrate surface typically is further aided by the chemical activity of the polishing composition (e.g., by oxidizing agents, acids, bases, or other additives present in the CMP composition) and/or the mechanical activity of an abrasive suspended in the polishing composition. Typical abrasive materials include silicon dioxide (silica), cerium oxide (ceria), aluminum oxide (alumina), zirconium oxide (zirconia), and tin oxide.
U.S. Pat. No. 5,527,423 to Neville, et al., for example, describes a method for chemically-mechanically polishing a metal layer by contacting the surface of the metal layer with a polishing slurry comprising high purity fine metal oxide particles suspended in an aqueous medium. Alternatively, the abrasive material may be incorporated into the polishing pad. U.S. Pat. No. 5,489,233 to Cook et al. discloses the use of polishing pads having a surface texture or pattern, and U.S. Pat. No. 5,958,794 to Bruxvoort et al. discloses a fixed abrasive polishing pad.
A semiconductor wafer typically includes a substrate, such as silicon or gallium arsenide, on which a plurality of transistors have been formed. Transistors are chemically and physically connected to the substrate by patterning regions in the substrate and layers on the substrate. The transistors and layers are separated by interlevel dielectrics (ILDs), comprised primarily of some form of silicon dioxide (SiO2). The transistors are interconnected through the use of well-known multilevel interconnects. Typical multilevel interconnects are comprised of stacked thin-films consisting of one or more of the following materials: titanium (Ti), titanium nitride (TiN), tantalum (Ta), aluminum-copper (Al—Cu), aluminum-silicon (Al—Si), copper (Cu), tungsten (W), doped polysilicon (poly-Si), and various combinations thereof. In addition, transistors or groups of transistors are isolated from one another, often through the use of trenches filled with an insulating material such as silicon dioxide, silicon nitride, and/or polysilicon.
Silicon carbide (SiC) is a material with a unique combination of electrical and thermo-physical properties that make it well-suited for use in an electronic device. As disclosed in WO 2005/099388 to Kerr et al., these properties include high breakdown field strength, high practical operating temperature, good electronic mobility and high thermal conductivity. Silicon carbide has a significantly greater hardness and relative chemical inertness compared to many other materials that comprise an integrated circuit. This greater hardness and chemical inertness makes the removal of silicon carbide using CMP techniques difficult. Removing silicon carbide with conventional CMP compositions and methods frequently results in the unwanted removal of other materials such as silicon dioxide.
Although many of the known CMP slurry compositions are suitable for limited purposes, the conventional compositions tend to exhibit unacceptable polishing rates and corresponding selectivity levels to insulator materials used in wafer manufacture. Known polishing slurries tend to produce poor film removal traits for the underlying films, or produce deleterious film-corrosion, which leads to poor manufacturing yields.
In addition, known polishing compositions and methods do not provide the ability to selectively remove silicon carbide from a semiconductor wafer without removing materials such as silicon dioxide from the same wafer at unacceptably high levels. As the technology for integrated circuit devices advances, traditional materials are being used in new and different ways to achieve the level of performance needed for advanced integrated circuits. In particular, silicon nitride, silicon carbide, and silicon dioxide are being used in various combinations to achieved new and ever more complex device configurations. In general, the structural complexity and performance characteristics vary across different applications.
There is an ongoing need to develop new polishing methods and compositions that provide relatively high rates of removal of silicon carbide and to selectively remove silicon carbide in preference to other materials present on the surface of the semiconductor wafer. The present invention provides such improved polishing methods and compositions. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.